Most of us do not think much about what goes into our teeth. We sit in the chair, wince at the drill and trust the person in the white coat to sort it out. But in 2025, the World Health Organisation released a landmark guideline that puts those quiet, routine decisions at the centre of a much larger story, one that connects your dental appointment to mercury pollution, climate commitments and the health of ecosystems you will never visit. It is a document aimed at clinicians and governments, written in the careful language of evidence grading and systematic reviews, but its implications are personal, practical and urgent for anyone who has ever had a filling or is likely to need one.
The guideline on environmentally friendly and less invasive oral health care for preventing and managing dental caries is, in plain language, a roadmap for getting mercury out of dentistry for good. It arrives at a pivotal moment, backed by years of accumulated scientific evidence and shaped by a growing international consensus that the materials we use to fix our teeth have consequences that ripple well beyond our mouths.
Dental caries, which is just the clinical name for tooth decay, is the most common non-communicable disease on the planet. It affects an estimated 2.7 billion people worldwide. That is more than a third of humanity walking around with a disease that begins, in many cases, in early childhood. Tooth decay is not merely a cosmetic inconvenience. It causes pain, affects a person’s ability to eat, speak and socialise, and carries a disproportionate burden among the poorest and most vulnerable communities who have the least access to dental care.
For more than 175 years, the standard solution to a cavity has been dental amalgam, a silver-coloured filling material that is roughly half mercury by weight. Mercury is one of the most toxic heavy metals known to science. It affects the nervous system, the kidneys, the immune system and the lungs. It can travel vast distances through the atmosphere, persist in ecosystems for generations and accumulate in fish and seafood in a form that is particularly dangerous to humans. Outside of dentistry, the world has been steadily trying to phase mercury out of products, from thermometers to fluorescent light bulbs. The Minamata Convention on Mercury, an international treaty named after a Japanese city devastated by industrial mercury poisoning in the 1950s, entered into force in 2017 with the specific aim of reducing humanity’s mercury footprint. Dental amalgam has been in its sights ever since.
The new WHO guideline does not simply say “stop using amalgam and use something else.” It does something more important. It provides clinicians, governments and health systems with clear, evidence-graded recommendations for what the alternatives are, how effective they are, and how to use them safely. That is no small feat. The guideline is built on a comprehensive programme of systematic reviews covering clinical effectiveness, cost, toxicology and environmental impact. It went through rigorous independent review. And it offers, for the first time, a coherent clinical picture of mercury-free dentistry from prevention all the way through to restoration.
So what does it actually recommend? The guideline identifies three main categories of intervention. The first is prevention, and the strongest recommendation in the entire document is disarmingly simple: fluoride varnish applied twice a year. This is a sticky, professionally applied coating that is painted onto the teeth, particularly in children and older adults, to strengthen enamel and prevent decay from taking hold. The evidence shows it prevents roughly 37 per cent of new cavities in baby teeth and around 43 per cent in adult teeth over three years. It is cheap, safe, requires minimal training to apply and can be delivered in schools, community centres or by nurses rather than dentists. For a disease that affects billions of people and costs the global economy staggering sums each year, this is the kind of low-tech, high-impact solution that public health has long needed.
The guideline also recommends silver diamine fluoride, a clear liquid that, when applied to a tooth, can stop active tooth decay in its tracks. Its main drawback is cosmetic: it turns the decayed area of the tooth permanently black. For a front tooth, that can understandably give a patient pause. But for a back molar in a five-year-old, or a root cavity in an elderly patient who cannot tolerate conventional drilling, it is close to a miracle. It requires no injection, no drill, no removal of tooth structure. A trained health worker can apply it with a small brush in under a minute. The WHO now recommends it both for prevention and for managing existing cavities in primary teeth and on the root surfaces of permanent teeth, with the evidence for those specific applications sitting at moderate certainty.
When a cavity has progressed too far for prevention or arrest and a restoration is genuinely needed, the guideline recommends two types of filling material: glass ionomer cements and resin-based composites. Glass ionomer is a tooth-coloured material that bonds chemically to the tooth, releases fluoride to protect against future decay and does not require the elaborate moisture control or specialised equipment that other materials demand. It is particularly suited to community-based care, to children and to older patients with complex medical histories. Resin-based composites, the white fillings that have become familiar in private dental practices, are harder, more durable and better at colour-matching the natural tooth. They are more technique-sensitive, meaning they require a skilled operator and proper equipment, and they carry some chemical considerations that the guideline addresses with unusual candour.
Those chemical considerations are worth understanding. Resin-based composites contain compounds derived from bisphenol A, commonly known as BPA. BPA is a chemical that the European Chemicals Agency classifies as a substance of very high concern because it can interfere with the body’s hormonal system. Hormones act as the body’s chemical messengers, regulating everything from growth and reproduction to metabolism and mood. Endocrine disruption, which is the scientific term for interference with these systems, is a particular risk during periods of hormonal development: in the womb, in infancy, in childhood and through adolescence. The WHO guideline recommends exercising caution with BPA-containing resin materials specifically in children, adolescents, pregnant women and breastfeeding mothers. This is not a cause for panic. The BPA that leaches from dental composites is measured in trace amounts far smaller than daily dietary exposure from food packaging. But the guideline applies what it calls the precautionary principle, meaning that where scientific uncertainty exists and the populations at risk are vulnerable, it is better to err on the side of caution. Around a third of composite materials on the market in 2023 contained no BPA derivatives at all, which means BPA-free alternatives already exist and should be the preferred choice for these groups.
The guideline also makes a practical point that deserves more attention than it typically receives in dental consultations: the most sustainable thing a dental practice can do for the environment is help patients avoid needing a filling at all. Prevention, whether through fluoride programmes, dietary sugar reduction or early detection of decay, is cheaper, less invasive, less environmentally costly and better for the patient than any restoration however clever its materials. The environmental footprint of a fluoride varnish applied during a scheduled check-up is negligible. A resin composite filling requires industrial manufacturing, uses electricity for curing, generates micro- and nanoparticles during polishing that can enter wastewater, and eventually finds its way into landfill or crematoria. None of this means composite fillings should not be used. It means the dental profession and the health systems behind it should be doing everything possible to ensure fewer people need them in the first place.
For most people sitting in a dental chair, this guideline will not immediately change what happens during an appointment. Change in clinical practice is slow, particularly in countries where dental education still emphasises drilling and filling over prevention and minimal intervention. But the guideline sends a clear directional signal to governments, dental schools, insurance systems and professional bodies. It puts the weight of the WHO’s global authority behind a model of dental care that prioritises keeping teeth healthy over restoring them once they are damaged, that recognises the dental surgery as part of a broader environmental and public health system, and that insists the materials used in that surgery should be safe not just for the patient on the chair but for the water, soil and ecosystems downstream.
For billions of people who have never had access to a dentist at all, some of these recommendations, particularly fluoride varnish and silver diamine fluoride applied by trained community health workers, could genuinely be transformative. For those in wealthier countries who can choose between materials, the guideline provides a more informed basis for that conversation with a clinician. And for policymakers who must decide how to spend limited health budgets, it offers clear evidence that prevention is both clinically effective and cost-effective in a way that restorative care, however necessary, simply cannot match.
The age of the silver filling may not be quite over. But its days are numbered, and what replaces it will be better for your teeth, your body and the planet that your children and grandchildren will inherit.
